EP0344760B1 - Rückgewinnung und Konzentration von wässerigen Säuren und Basen - Google Patents

Rückgewinnung und Konzentration von wässerigen Säuren und Basen Download PDF

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Publication number
EP0344760B1
EP0344760B1 EP89109877A EP89109877A EP0344760B1 EP 0344760 B1 EP0344760 B1 EP 0344760B1 EP 89109877 A EP89109877 A EP 89109877A EP 89109877 A EP89109877 A EP 89109877A EP 0344760 B1 EP0344760 B1 EP 0344760B1
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Prior art keywords
emulsion
reagent
aqueous
membrane
phase
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French (fr)
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EP0344760A3 (en
EP0344760A2 (de
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Robert P. Cahn
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Stantech GmbH
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Stantech GmbH
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/42—Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
    • B01D61/44—Ion-selective electrodialysis
    • B01D61/445—Ion-selective electrodialysis with bipolar membranes; Water splitting
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/38—Liquid-membrane separation
    • B01D61/40—Liquid-membrane separation using emulsion-type membranes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S210/00—Liquid purification or separation
    • Y10S210/902—Materials removed
    • Y10S210/908—Organic
    • Y10S210/909—Aromatic compound, e.g. pcb, phenol

Definitions

  • the invention relates to the selective removal of dissolved acids or bases from aqueous solutions and their subsequent recovery in concentrated form. This is achieved by a combination of liquid membrane extraction using a selective reagent and by bipolar membrane electrolysis of the spent selective reagent.
  • liquid membrane emulsions may be used to remove dissolved substances from aqueous solutions; see for example, U.S. Pat. Nos. 3,617,546; 3,637,488; and 3,779,907.
  • the emulsion is characterized as having a dispersed or internal phase suspended in a continuous phase.
  • the continuous phase of the emulsion is immiscible with the aqueous solution but is permeable to the dissolved substance.
  • the dispersed phase which usually is miscible with the aqueous phase, contains a reagent which cannot permeate through the continuous phase, but is capable of reacting with the dissolved substance when it reaches the dispersed phase to form a product which cannot permeate back through the continuous phase.
  • the emulsion is contacted with the aqueous solution, whereupon the dissolved substance permeates through the continuous phase into the dispersed phase and is retained therein.
  • the phenate ion is insoluble in oil, and, therefore, cannot permeate back into the external dilute aqueous solution.
  • the weak acid, phenol it can be removed from a dilute aqueous solution by means of a liquid membrane emulsion containing a base.
  • a second method is recovery of the phenol from the spent caustic by treatment with a strong acid, such as sulfuric acid, which will liberate the phenol, leaving behind a solution of sodium sulfate, which is much easier to dispose of than sodium phenate. While this method recovers phenol as a salable product, it requires the use of an additional reagent, e.g. sulfuric acid. Consequently, for each mole of phenol removed, at least one mole of caustic and one half mole of sulfuric acid are consumed, and returned to the environment as undesirable sodium sulfate. In practice, incomplete utilization of the caustic in the phenol extraction necessitate the use of greater than stoichiometric amounts of both caustic and sulfuric acid.
  • a strong acid such as sulfuric acid
  • Another method, and the subject of the present invention is the splitting up of the sodium phenate salt formed into (1) phenol, which is separated, purified and used as a chemical, and into (2) caustic solution, which is recycled to the phenol removal step by reemulsification to form regenerated liquid membrane emulsion.
  • a preferred method of achieving this splitting up is by the use of bipolar membrane electrolysis, allowing the sodium phenate feed solution recovered from the spent liquid membrane emulsion to be converted into one stream which is rich in caustic, and another stream rich in phenol.
  • Said bipolar membrane electrolysis is disclosed in H. Strathmann, H. Chmiel, Chem.-Jng.-Tech. 56 (1984) Nr.3, pp. 214-220.
  • the stream rich in caustic generated by this technique is reused as recycled regenerated liquid membrane emulsion, it is not necessary to achieve a high degree of purity of the regenerated caustic.
  • the regenerated caustic can still contain some phenol, provided that there is sufficient unreacted caustic in this stream to make emulsification and reuse worthwhile.
  • the regenerated phenol solution need not be entirely free of caustic, since the free phenol will removed from this solution first by phase separation, followed by steam stripping.
  • liquid membrane extraction exhibits selectivity between different dilute acids or bases, allowing separate removal and recovery of different contaminants or solutes present in the dilute aqueous feed solution. Simple direct electrolysis of the dilute feed liquor could not achieve this separation.
  • Another advantage of this technique is that dilute solutions can be converted into concentrated products, since the liquid membrane extraction step per se is a concentration step, vastly increasing the concentration of the acid or base in the incoming feed. Direct bipolar membrane electrolysis would not achieve such a concentration. Further, electrolysis of a dilute solution has to overcome large resistance losses on account of the low conductivity of dilute aqueous solutions, a problem neatly avoided by the present technique, which electrolyzes a concentrated (e.g., spent caustic) solution.
  • a further advantage of the present technique is that it allows the use of internal reagents in the liquid membrane system which cannot be considered for environmental or economic reasons in a throw-away situation, such as simple discarding of the spent internal phase of the used emulsion. Also, reagents can be used which have better solubility properties than the reagent generally used in a throw-away situation.
  • the use of potassium hydroxide is a case in point, compared to the more usual caustic soda, or, in the case of amine removal, use of hydrochloric rather than sulfuric acid.
  • a further advantage is that the new combination permits the use of more environmentally acceptable, although more expensive reagents in the internal phase of the emulsion.
  • a small quantity of the internal phase will leak out into the aqueous phase being treated, resulting in minuscule, yet measurable contamination of the aqueous treating effluent.
  • economics usually dictate the use of the lowest cost reagent.
  • Reagent cost and effluent contamination considerations do not necessarily point to the same reagent. With the use of the present invention, cost considerations for the used reagent can be disregarded, making the choice of an environmentally least objectionable reagent so much easier.
  • the aqueous liquid feed containing said acid is contacted in an agitated vessel with dispersed globules of a water-in-oil emulsion, where the continous (oil) phase of the emulsion contains a surfactant and possibly an acid solubilizer, and the encapsulated dispersed aqueous phase of the emulsion contains a base which can neutralize any permeated acid.
  • the undissociated acid will keep on permeating through the oil film into the internal droplets, where the base will convert the undissociated acid into an oil-insoluble salt.
  • the emulsion is allowed to settle away from the treated feed solution which is discarded or subjected to further treatment.
  • the emulsion is broken, using one or a combination of several means of separation, such as centrifugation, agitation, addition of chemicals, or electrostatic coalescence.
  • the preferred method of separating the emulsion phases is by means of an electrostatic coalescer (cf. US-A-4 283 290).
  • the internal aqueous phase broken out of the emulsion is further treated as described hereinbelow, while the recovered oil phase is recycled to emulsion making and thus reused directly in the process.
  • the spent internal reagent solution comprising salt and left-over (excess) reagent, e.g. base
  • the bipolar membrane electrolysis is the bipolar membrane, which consists of an anion-permeable anion-exchange resin layer, and a cation-permeable cation-exchange resin layer, sandwiched together.
  • the membrane is also somewhat water permeable. When such a membrane is immersed into an aqueous solution, and a potential is applied across it, water at the interface between the two layers will be split into protons and hydroxyl ions.
  • the protons will migrate through the cation-permeable side (which must be the side closer to the cathode of the applied field) and the hydroxyl ions will drift to the anode via the anion-permeable layer.
  • the cell compartment adjacent to the cation-permeable layer will become enriched in protons, thus turning acidic, while the compartment adjacent to the anion-permeable layer will become enriched in hydroxyl ions, i.e. it will turn alkaline.
  • bipolar electrolysis requires a much lower voltage per unit cell than conventional electrolysis, about half the voltage or less, with a corresponding saving in electric power consumption.
  • the dissolved substance which was removed from the dilute aqueous solution feed by means of the reagent-loaded liquid membrane emulsion, is regenerated in the bipolar membrane cell, separated from the reagent, as a much more concentrated aqueous solution than in the original feed.
  • the regenerated dissolved substance as a result of the separation achieved by the selective liquid membrane extraction, will also be free of other contaminants which accompanied it in the dilute aqueous feed, and which frequently interfere with any attempts to recover it directly from the dilute feed. From the said more concentrate aqueous solution, the dissolved substance can be recovered economically by any number of conventional means such as phase separation, extraction, distillation, steam stripping, etc.
  • This process is eminently suited to the recovery of dilute acids and bases from aqueous solutions in which they are admixed with other materials, frequently other acids and bases, from which they can be separated by the emulsion liquid membrane technique.
  • a slightly acidic compound from its dilute aqueous solution also containing other acids or their anions, such as sulfuric acid or sulfate ion, chloride, nitrate, phosphate, etc.
  • a preliminary emulsion liquid membrane separation using an aqueous caustic-containing emulsion will pull the phenol selectively out of this dilute solution.
  • the other anions and their respective acids which are all essentially oil-insoluble, will not permeate into the internal droplets of the emulsion through the oil membrane, effecting a very selective separation of the phenol from the other acids in the original feed.
  • Demulsification of the spent emulsion and bipolar membrane electrolysis of the spent internal aqueous phase of the emulsion will liberate the extracted phenol and regenerate the spent caustic for reuse. Since the concentration of phenol in the spent emulsion can be very much higher than its concentration in the incoming feed, recovery of the phenol as a product is much simpler than if this recovery had been attempted on the incoming feed.
  • Another feature of the present invention is that if bipolar electrolysis of the incoming feed were attempted, the recovered acid would not be just phenol, but would also include sulfuric, hydrochloric, phosphoric and other acids present as such or as their anions in the incoming feed. Not only would this result in a highly contaminated product, requiring further purification, but it would also involve the expenditure of unnecessary quantities of power to regenerate the undesired contaminant acids, e.g. the sulfuric, hydrochloric and phosphoric acids.
  • solubilizers may be oil-soluble clathrating, complexing, chelating or ion exchange materials which may be selective to one or several cations or anions in the aqueous feed.
  • such materials may be DHPA, di(ethylhexyl)phosphoric acid or a chelating agent for copper, for example LIX64NTM, a material supplied by General Mills Chemical Co, and for anions Amberlite LA-2TM, an oil-soluble secondary amine manufactured by Rohm & Haas, or other materials which provide the requisite solubility and selectivity to the membrane phase.
  • inorganic acids and, of course their anions are essentially insoluble in the undoped membrane phase, and are consequently prevented from being picked up by the liquid membrane emulsion.
  • organic acids such as acetic, propionic, butyric, benzoic, and other naphthenic or aromatic acids, phenol etc. are sufficiently soluble in oil to give some permeability to the undissociated form (not the ionic form) of the acid.
  • a few inorganic acids, or their anhydrides, e.g. hydrogen sulfide, carbon dioxide, or sulfur dioxide have some oil solubility and, therefore, permit selective removal of these acids in the presence of strong acid contaminant such as sulfuric and hydrochloric acids.
  • Figure 1 is a schematic representation of a preferred embodiment of the process of the present invention.
  • Figure 2 is a cross-section through a unit cell for bipolar membrane electrolysis which is a part of the preferred embodiment shown in Figure 1.
  • the present invention relates to a process for the selective removal of dissolved lipophilic organic acids and/or bases from an aqueous feedstream contaminated with inorganics, wherein
  • the preferred embodiment of the present invention is a process for the removal of a lipophilic organic acid or base dissolved in the aqueous feedstream.
  • a lipophilic organic acid specifically phenol
  • a strong base specifically caustic soda
  • Lipophilic organic bases provided the selected reagent is a strong acid, like sulfuric acid, follow an identical pattern. It should also be understood that while the following description is based on the removal of a single compound, several compounds, i.e. several lipophilic organic acids or several lipophilic organic bases, can be removed at the same time.
  • FIG. 1 shows a schematic of the general flowplan of the invention.
  • Fresh aqueous feed 1 containing a dissolved acid or base, in this case phenol, is fed to liquid membrane (LM) treater 2 where feed 1 is contacted with fresh LM emulsion 14 prepared in emulsifier 13.
  • the emulsion consists of a continuous or membrane phase, which is immiscible with feed 1 and a dispersed phase.
  • the membrane phase is usually a hydrocarbon based composition comprising petroleum-based solvents, such as paraffins, kerosene, naphthalenes or aromatics, as well as 0,1 - 5 wt.
  • oil-soluble detergents such as ENJ-3029, manufactured by Exxon Chemical Co.
  • a solubilizer for the compound or ion to be removed such as LIX64NTM when copper ion is to be removed, or AlamineTM, supplied by General Mills Chemical Co. when an oil-insoluble anion is to be removed.
  • LIX64NTM when copper ion is to be removed
  • AlamineTM supplied by General Mills Chemical Co.
  • the dispersed phase is an aqueous solution comprising a reagent, which will react with the dissolved substance diffusing through the membrane phase into the dispersed internal phase of the emulsion, preventing said substance to diffuse back out again, thus concentrating the dissolved substance in the dispersed phase droplets.
  • said reagent is caustic soda, NaOH, which may be present in the internal phase of the fresh emulsion in a concentration of 1-20 wt.%.
  • Other strong, oil insoluble bases like KOH, LiOH, K2CO3, and mixtures of these compounds can be used.
  • feed 1 and fresh emulsion 14 are contacted in a cocurrent or countercurrent manner for a sufficient length of time to assure the desired degree of removal of the dissolved compound, i.e. phenol from the feed.
  • this removal occurs, since the compound, being soluble in the membrane phase of the emulsion, will diffuse through this membrane phase into the internal droplets of the emulsion driven by a concentration gradient of the dissolved compound across the membrane phase, as long as the reagent is available to consume the compound as it arrives in the dispersed droplets, and as long as the concentration of the dissolved compound in the external feed phase is higher than the concentration of this compound in the internal dispersed droplets of the emulsion.
  • countercurrent contacting between emulsion and feed is frequently employed.
  • the time required for removal of the compound to the extent desired depends on the compound, the extent of removal, the treat ratio of emulsion to feed, and the type of contacting and agitation provided in treater 2. The time can vary from the order of 1 minute to as much as 30 minutes.
  • the minimum amount of emulsion used for the treating step is that which contains just sufficient reagent to react completely with the amount of compound to be removed from the feed. Any additional emulsion will enhance the driving force and improve contacting.
  • the mixture 3 of feed and emulsion are separated in settler 4, unless this phase separation is inherent in the operation of the LM treater 2, such as in a countercurrent tower.
  • settler 4 spent emulsion 6 is separated from treated feed 5. The latter is removed from the system for further processing or discharge, while the spent emulsion 6 is fed to coalescer 7 for emulsion phase separation.
  • Coalescer 7 can operate on a number of demonstrated principles to demulsify the emulsion and allow separation of the two phases. Centrifugation to separate out clear excess external, i.e. membrane phase, coupled with mechanical agitation of the resultant heavy emulsion and recycle to the centrifugation step was shown to be one way to break the emulsion. Another method involves adding chemical solvents to the emulsion which result in breaking the emulsion into two phases, from which the solvents can be recovered by distillation. Lastly, electrostatic coalescing has been shown to be a very successive and simple method to recover the separate phases. This method is best performed with insulated electrodes, under a potential field of 10-30 kV and applying an AC of a frequency between 10 and 15000 Herz. Electrostatic coalescence is the preferred method of breaking liquid membrane emulsions.
  • the membrane phase 8 separated out in the coalescer is recycled directly to the emulsifier 13 to regenerate fresh emulsion, as will be discussed below.
  • the spent internal phase 9 is withdrawn from coalescer 7 and fed to the bipolar membrane electrolysis cell 10.
  • the spent internal reagent is regenerated as stream 11 and the dissolved substance, whether acid or base, which had been extracted from feed 1 into the liquid membrane emulsion 14 in treater 2 is produced as a separated stream 12, either as such, or in aqueous solution, but at a much higher concentration than present in the original feed 1.
  • sodium phenate solution which is the internal phase of the spent emulsion, is effectively converted into sodium hydroxide solution and a relatively concentrated aqueous solution of phenol.
  • Fig. 2 The operation of the bipolar membrane cell is illustrated in Fig. 2 for the specific case of converting the aqueous sodium phenate internal reagent solution of the spent emulsion into (a) an aqueous sodium hydroxide stream suitable for recycle to the emulsifier for preparation of fresh emulsion, and into (b) a concentrated solution of phenol in water suitable for phenol recovery by any of a number of conventional means, such as phase separation, distillation, steam stripping, or a combination of the above.
  • the unhatched rectangles represent cross-sections through membranes which only allow passage of negative ions, i.e. anion-permeable membranes, while cross-hatched rectangles signify membranes which only allow positive ions, i.e. cations to pass through.
  • Such membranes are commercially available, and are frequently made from such a resins as polystyrene which can be sulfonated or otherwise provided with charged sidechains, such sulfonate groups or amine groups, which allow positive or negative ions, respectively, to permeate through the resin.
  • Membranes which are indicated by both an unhatched and a cross-hatched rectangle are bipolar membranes, where one side of the membrane is permeable only to cations, while the other side is only anion permeable.
  • a membrane When such a membrane is immersed in water, which is permeable through all of the above membranes, and an electric potential is applied across the membrane, water will dissociate into protons and hydroxide ions at the interface of the anion-permeable and cation-permeable membrane sides, and protons will migrate through the cation-permeable side of the bipolar membrane towards the cathode, while hydroxide ions will migrate in the opposite direction, through the anion-permeable side of the bipolar membrane, towards the anode.
  • bipolar membrane This property of the bipolar membrane is utilized in the bipolar electrolytic cell illustrated in Fig. 2 to carry out the decomposition of the salt in the spent internal reagent of the instant invention, sodium phenate in this example, into its constituent acid and base, phenol and sodium hydroxide, respectively.
  • the heart of the electrolytic cell is the bipolar membrane 21 which is placed, as shown, between anode 26 and cathode 27 in such a way that the anion-permeable side of membrane 21 faces the anode and the cation-permeable side faces the cathode.
  • OH ⁇ ions will issue from the bipolar membrane in the direction of the anode, and H+ ions will issue in the cathode direction.
  • a cation-selective membrane 22 is placed in the cell on the anode side of 21, and an anion-selective membrane 23 is put between 21 and cathode 27.
  • an aqueous stream 32 introduced into the cellular space 38 between membranes 21 and 23 will be enriched in H+ ions issuing from the bipolar membrane 21 and phenate ions PhO ⁇ passing through anion-selective membrane 23, as a result of feeding a spent internal reagent stream 33 into the space 39 between membrane 23 and cathode 27. Consequently, stream 25 issuing from cell compartment 38 between membranes 21 and 23 will be enriched in phenol.
  • Cell compartment 38 is, therfore, an acid-generating compartment.
  • bipolar electrolysis into the constituent acid and base of the contained salt only requires cell voltages of the order of 2 volts per unit cell.
  • Many of such repeating unit cell arrangements can be put in series between the anode 26 and cathode 27, as is shown schematically by dots 29 and 30, to make up a battery of electrolytic cells.
  • Such a battery arrangement would have repeating membranes ... 22-21-23-22-21-23-22-21-23 ... etc. placed between an anode 26 and a cathode 27, thus forming repeated cell compartments ... 37,38,39,37,38,39 .. . Note that compartments 36 and 39 are equivalent.
  • Spent internal reagent such as stream 28 or 33 would be fed into compartments 39 in the above described arrangement, and water or an aqueous stream would be fed into compartments 37 and 38.
  • Regenerated internal reagent an aqueous solution of sodium hydroxide in this case, will issue from all base-generating cell compartments 37, and recovered phenol, in aqueous solution or suspension, will leave the cells from the acid-generating compartments 38.
  • the liquid leaving the compartments 39, corresponding to streams 34 or 35 will be solutions of much lower sodium phenate salt content than present in the spent internal reagent fed to the cell, since Na+ ions migrated out of this stream through membrane 22, and phenate ions migrated out in the opposite direction through membrane 23.
  • Compartments 39 can be considered salt-depleting compartments.
  • the effluent solution since it is still rich in contained unconverted sodium phenate, containing between 5 % to 80 % of the sodium phenate in the spent internal reagent 28 or 33, will represent a disposal problem.
  • This stream will also comprise any unused sodium hydroxide from the liquid membrane permeation, i.e. base which was not consumed in the extraction step to neutralize phenol permeating into the internal aqueous reagent droplets. It is particularly advantageous to recycle this stream to the cell, specifically as streams 31 or 32, but preferably as stream 31.
  • Stream 25 which is an aqueous stream rich in phenol, goes to a phenol recovery operation, not specifically shown in Figure 1, where the regenerated phenol is recovered as mentioned beforehand by conventional means, such as distillation, phase separation, extraction or steam stripping.
  • the aqueous raffinate from this operation will still contain small amounts of unrecovered phenol, and it is advantageous to use this stream as aqueous make-up stream 32 feeding the cell compartments 38 regenerating phenol and generating streams 25.
  • the recycle of these streams to the bipolar membrane cell as feed stream to acid and base-generating compartments is a particularly beneficial aspect of the present invention. It shows how the combination of bipolar membrane electrolysis and liquid membrane extraction surprisingly and synergistically improve each other by allowing weak points in each process to be strengthened. For example, this recycle of partially converted salt solution to the acid and base-generating compartments of the bipolar membrane cell overcomes the difficulty of that process that incomplete conversion of the salt results in process inefficiencies, environmental disposal problems, and frequently inefficient operation if high conversion is required to avoid this disposal problem.
  • the bipolar cell diminishes the demand on the performance of the liquid membrane extraction process, on the utilization of the internal reagent, and allows the use of reagents which would be considered unacceptable on a once-through basis, be it for reasons of availability, cost, contamination or convenience. In addition, of course, it permits the recovery of the dissolved acid or base, which, up to now, had not been considered a feasible operation.
  • weak acids which satisfy this condition of permeability are generally organic acids like phenols, carboxylic acids, and certain inorganic acids which are soluble in hydrocarbons, including hydrogen sulfide, hydrogen cyanide, and carbon dioxide or sulfur dioxide.
  • Weak bases include ammonia, amines and many organic nitrogen compounds of a basic nature. Strong acids and bases which are suitable as treating agents encapsulated in the liquid membrane are inorganic acids and bases, e.g. sulfuric, hydrochloric and nitric acids, as well as the alkali and alkaline earth oxide based hydroxides. These materials are usually sufficiently highly ionized so that their membrane solubility is very low.
  • the aqueous feed 1 comprising a dilute dissolved acid or base, referred to as a dissolved substance
  • a dissolved substance is treated with a fresh liquid membrane emulsion 14 in treater 2 to remove from 20 % to 99.99 %, preferably 90 to 99.99 % of said dissolved substance from feed 1.
  • the treated feed 5 is withdrawn from the system after separation from the liquid membrane emulsion in settler 4 or the like.
  • the fresh liquid membrane emulsion 14 comprises a continuous oil or membrane phase and a dispersed aqueous internal phase which contains a reagent capable of neutralizing said dissolved substance and preventing its escape from the emulsion once it has permeated into the dispersed droplets of the internal phase.
  • the amount of said reagent in said fresh emulsion 14 will be between 1.01-3 times the stoichiometric amount of said reagent required to neutralize the dissolved substance removed in the liquid membrane treating operation 2, preferably between 1.01-1.5 times the stoichiometric amount, most preferably between 1.1 and 1.5 times the stoichiometric amount.
  • the spent emulsion 6 removed after the treating operation from the treated feed 5 will comprise a spent internal phase 9 which is separated from a continuous membrane phase in a coalescer 7 and sent to bipolar membrane electrolysis 10 where the internal reagent is regenerated and the extracted dissolved substance 12 is recovered.
  • the spent internal reagent 9 is an aqueous solution comprising the recovered dissolved substance in the form of a salt with the reagent, together with between 0.01 and 2, preferably between 0.01 and 0.5, and most preferably between 0.1 and 0.5 times the stoichiometric amount of free, unneutralized reagent, compared with the amount of reagent required to neutralize the dissolved substance removed in the LM treater 2.
  • the spent internal reagent 33 at first passage through the cell via compartment 39, will leave the cell as a stream 35, depleted in the salt formed from the dissolved substance recovered in treater 2 and the said internal reagent, but still comprising between 0.01 and 2 times the said stoichiometric amount of excess internal reagent, and also comprising some excess salt which may have been present in the internal reagent phase of the fresh emulsion 14.
  • This excess salt which circulates around in the fresh and spent emulsion, may be between 0.01 and 2 times the amount of salt formed by neutralization in LM treater 2.
  • the salt depleted stream 35 can be discarded, but preferably it is fed to the reagent-regenerating compartment of the bipolar membrane cell.
  • the reagent is a base
  • the reagent is an acid
  • the corresponding stream is 32 flowing through compartment 38.
  • the stream leaving the reagent-regenerating compartment will be an aqueous solution comprising between 1.01 and 3 times the stoichiometric amount of said reagent, and between 0.01 and 2 times the stoichiometric amount of salt, as discussed above.
  • This stream is the regenerated internal reagent phase 11 of Figure 1, ready for recycle to emulsifier 13.
  • the dissolved substance-regenerating compartment of the bipolar membrane electrolysis cell if it is fed with a aqueous stream comprising between 0.01 and 0.5 times the amount of dissolved substance removed in treater 2, will regenerate essentially all of the removed dissolved substance, so that the stream leaving this cell compartment will comprise between 1.01 and 1.5 times the amount of dissolved substance removed in the LM treater.
  • the dissolved substance is an acid
  • the feed to the compartment corresponds to stream 32 in Fig. 2
  • the dissolved substance-regenerating compartment is 38
  • the effluent corresponds to stream 25.
  • the feed to the compartment corresponds to stream 31 in Fig. 2
  • the compartment is 37
  • the effluent corresponds to stream 24.
  • the effluent next goes for treatment to a dissolved substance recovery unit where the recovered dissolved substance is taken out of effluent stream 25 or 24, as the case may be.
  • the amount of dissolved substance taken out of this stream is, at best, equal to the amount of dissolved substance removed in treater 2, so the amount of dissolved substance left in the treated effluent is between 0.01 and 0.5 times the amount of dissolved substance taken out in treater 2.
  • said treated effluent is a preferred feed to the dissolved substance-regenerating compartment of the bipolar membrane cell.
  • the regenerated internal reagent phase 11 and membrane phase 8 separated out in coalecer 7 are combined in emulsifier 13 to form fresh emulsion 14.
  • the emulsion usually comprises an intimate mixture of the two phases, aqueous as the internal, dispersed phase, and oil as the continuous membrane phase in the volume ratio of between 10:1 and 1:10.
  • the membrane phase comprises a hydrocarbon or mixture of hydrocarbons in the C7 to C20 range, together with a surfactant such as ENJ-3029 manufactured by Exxon Chemical Co.
  • the surfactant concentration can range from 1 to 5 wt.% in the membrane phase.
  • the membrane phase may also contain an oil soluble ion exchange resin, complexing agent or modifier to improve the solubility of the dissolved substance in the membrane phase, and thus to enhance the permeability of the dissolved substance through the membrane phase in the emulsion.
  • Suitable substances are complexing agents like LIX64NTM marketed by General Mills Chemical Co., suitable for metal ions such as copper, AlamineTM (also manufactured by General Mills) for anion transfer, ethylene diamine tetraacetic acid (EDTA) for cation transfer, aliphatic alcohols to improve the solubility of organic acids in the membrane phase, and the like.
  • An aqueous waste stream flowing at the rate of 1000 l/h has a phenol content of 200 wt. ppm. It is fed to a liquid membrane extraction step, where it is contacted with a liquid membrane emulsion comprising as internal, dispersed reagent a 5 wt.% aqueous NaOH solution, also comprising 3.87 wt.% sodium phenate, and as membrane phase an oil phase comprising S100N, a hydrocarbon of about 35 carbon number and about 9 % aromatics content, and as surfactant comprising 2 wt.% ENJ-3029.
  • a liquid membrane emulsion comprising as internal, dispersed reagent a 5 wt.% aqueous NaOH solution, also comprising 3.87 wt.% sodium phenate, and as membrane phase an oil phase comprising S100N, a hydrocarbon of about 35 carbon number and about 9 % aromatics content, and as surfactant comprising 2 wt.% ENJ-3029.
  • the ratio of membrane phase to aqueous phase in the emulsion is 2/1 by volume, and the emulsion is fed to the treater at the rate of 5.85 l/h.
  • the treat ratio of emulsion to feed in the reactor is maintained at 1/5 vol/vol, but treated feed and spent emulsion are removed from the treating step by differential settling at the reate at which they are fed and accumulating, i.e. 1000 l/h for the treated feed, and about 6 l/h for the spent emulsion.
  • the treater 98 % of the phenol is removed, so the treated feed will contain 4 wt. ppm of phenol.
  • Table 1 The composition of the aqueous phase in the fresh and spent emulsion is as shown in Table 1.
  • the spent emulsion is broken, using an electrostatic coalescer, and the spent aqueous phase of composition as shown in Table 1 is sent to a bipolar membrane electrolytic cell operating at 2 V per unit cell potential.
  • the spent aqueous phase is first sent through the salt-depletion compartment of the cell, where the salt content of the solution is reduced.
  • the salt-depleted solution is then fed to the caustic-regenerating compartment of the cell, where caustic is increased back to the level in the aqueous phase of the fresh emulsion.
  • Table 2 Compositions of internal aqueous phase in bipolar cell g/h Spent Aqueous Salt-Depleted Aq. Fresh emulsion NaOH 20.85 20.85 104.26 Na phenate 322.50 80.62 80.62 Water 1937.75 1937.75 1900.22 Total 2281.10 2039.22 2085.10
  • aqueous solution containing about 0.5 wt % of phenol is fed to the phenol-generating compartment of the bipolar cell, where it is enriched in phenol which is being removed from the spent aqueous phase passing through the cell.
  • the effluent from this cell compartment will contain about 4.8 wt. % phenol.
  • This stream is sent to a phenol recovery unit, which treats this stream by steam stripping and distillation to remove the bulk of the phenol contained therein and recover it as pure phenol.
  • the stripped residue is an aqueous solution containing about 0.5 wt % phenol, which is recycled to the phenol-generating compartment as described hereinabove.
  • An aqueous waste stream flowing at the rate of 1000 l/h has a phenol content of 200 wt. ppm. It is fed to a liquid membrane extraction step, where it is contacted with a liquid membrane emulsion comprising as internal, dispersed reagent a 5 wt. % aqueous NaOH solution, and as membrane phase an oil phase comprising S100N, a hydrocarbon of about 35 carbon number and about 9 % aromatics content, and as surfactant comprising 2 wt. % ENJ-3029.
  • the ratio of membrane phase to aqueous phase in the emulsion is 2/1 by volume, and the emulsion is fed to the treater at the rate of 5.80 l/h.
  • the treat ratio of emulsion to feed in the reactor is maintained at 1/5 vol/vol, but treated feed and spent emulsion are removed from the treating step by differential settling at the rate at which they are fed and accumulating, i.e. 1000 l/h for the treated feed, and about 6 l/h for the spent emulsion.
  • the treater 98 % of the phenol is removed, so the treated feed will contain 4 wt. ppm of phenol.
  • the composition of the aqueous phase in the fresh and spent emulsion is as shown in Table 3.
  • the spent emulsion is broken, using an electrostatic coalescer, and the spent aqueous phase of composition as shown in Table 1 is sent to disposal. Two alternate disposals can be carried out:
  • a sodium phenate solution of composition equal to that of the spent aqueous internal reagent phase shown in Table 1 of Example 1 is sent to a bipolar membrane electrolysis cell where 75 % of the salt is decomposed into its constituent sodium hydroxide and phenol.
  • the salt-depleted effluent from this operation has the composition shown in Table 2 of Example 1 under "Salt-depleted aq.”, and is discarded.
  • Recovery of additional phenol and caustic from this stream requires much higher than 2 V potential and results in considerable amounts of impurities being introduced into the caustic and phenol product streams, specifically phenol into the caustic-stream, and caustic into the phenol stream.
  • the discard of the salt-depleted effluent not only intails a loss of caustic and phenol, but also involves disposal of an environmentally harmful fluid.
  • the recoverd caustic is relatively dilute, about 5 wt. % and represents a stream of marginal market value.
  • Example 1 shows how the process of the present invention operates beneficially in a specific, though not limiting example, reducing a contaminant in a waste water stream, with minimal requirements of chemicals, with the potential production of the waste product as a marketable commodity, and without the formation of waste streams which are disposal problems in themselves.
  • Example 2 illustrates that liquid membrane emulsion treatment by itself achieves the contaminant reduction, but requires considerable chemical make-up and introduces waste disposal problems of its own.
  • Example 3 and 4 show that bipolar electrolysis alone will not solve the contaminant removal problem, while Example 4 further demonstrates that bipolar electrolysis of a concentrated sodium phenate solution, by itself, is not a chemically efficient nor an environmentally satisfactory operation.

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  • Engineering & Computer Science (AREA)
  • Water Supply & Treatment (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Health & Medical Sciences (AREA)
  • Urology & Nephrology (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
  • Water Treatment By Electricity Or Magnetism (AREA)
  • Extraction Or Liquid Replacement (AREA)

Claims (8)

  1. Verfahren zur selektiven Entfernung gelöster lipophiler organischer Säuren und/oder Basen aus einem mit anorganischen Stoffen verunreinigten wäßrigen Speisestrom, worin
    (a) der Speisestrom mit einer Emulsion in Berührung gebracht wird, die eine geschlossene Membran-Phase, die mit dem Speisestrom nicht mischbar, jedoch für die ungeladenen Species der organischen Säuren und Basen durchlässig ist, und eine dispergierte wäßrige Phase aufweist, die zwischen dem 1,01-fachen und dem 3-fachen der stöchiometrischen Menge eines zur Ionisierung erforderlichen Reagens enthält, wobei die Substanzen in dieser Form nicht befähigt sind, die Membran-Phase der Emulsion rückwärts zu durchdringen, unter Bedingungen, die die Absorption von 20 bis 99,99 % der lipophilen organischen Säuren und Basen aus dem Speisestrom in die Emulsion ermöglichen;
    (b) die Emulsion nach der Behandlung gemäß Schritt (a) aus dem Speisestrom entfernt wird und die abgetrennte Emulsion zu der geschlossenen Membran-Phase und der dispergierten wäßrigen Phase demulgiert wird,
    dadurch gekennzeichnet, daß das Verfahren in der Weise kontinuierlich durchgeführt wird, daß
    (c) die demulgierte dispergierte wäßrige Phase aus Schritt (b) einer bipolaren Membran-Elektrolyse unterzogen wird, worin die Zelle
    (i) wenigstens einen Salz-abreichernden Raum, in den die dispergierte wäßrige Phase zugeführt wird,
    (ii) wenigstens einen Reagens-regenerierenden Raum und
    (iii) wenigstens einen die gelöste Substanz regenerierenden Raum, in dem zwischen 20 und 95 % des der Zelle zugeführten Salzes in ein Reagens zur Umlaufführung in den Schritt (d) und in zurückgewonnene gelöste Substanz umgewandelt wird,
    aufweist, wobei wenigstens ein Teil der aus dem Salzabreichernden Raum der Zelle abfließenden Flüssigkeit dem Reagens-regenerierenden Raum der Zelle zugeführt wird und die aus dem die gelöste Substanz regenerierenden Raum abfließende Flüssigkeit der weiteren Verarbeitung durch einen Rückgewinnungs-Schritt unterzogen wird, um die gelöste Substanz aus der abfließenden Flüssigkeit zurückzugewinnen; und
    (d) der Reagens-reiche wäßrige Strom aus Schritt (c) durch Emulgieren mit der Membran-Phase aus Schritt (b) zur Bildung der in Schritt (a) eingesetzten Emulsion vereinigt wird.
  2. Verfahren nach Anspruch 1, worin, wenn die zu extrahierende gelöste Substanz eine lipophile organische Säure oder eine Anzahl lipophiler organischer Säuren ist, das Reagens zur Ionisierung in (a) eine starke anorganische Base ist.
  3. Verfahren nach Anspruch 1, worin, wenn die zu extrahierende gelöste Substanz eine lipophile organische Base oder eine Anzahl lipophiler organischer Basen ist, das Reagens zur Ionisierung in (a) eine starke anorganische Säure ist.
  4. Verfahren nach irgendeinem der Ansprüche 1 bis 3, worin die Menge des Reagens zwischen dem 1,01-fachen und dem 1,5-fachen der stöchiometrischen Menge des zur Ionisierung der Menge der gelösten Substanz, die durch die Emulsion in Schritt (a) absorbiert wird, erforderlichen Reagens liegt.
  5. Verfahren nach irgendeinem der Ansprüche 1 bis 4, worin die Menge der gelösten Substanz, die aus dem Speisestrom in Schritt (a) entfernt wird, zwischen 90 und 99,98 % der Menge der gelösten Substanz in dem Speisestrom liegt.
  6. Verfahren nach irgendeinem der Ansprüche 1 bis 5, worin zwischen 50 und 90 % des der bipolaren Membran-Elektrolyse-Zelle zugeführten Salzes in Reagens zur Umlaufführung in den Schritt (d) und in die zurückgewonnene gelöste Substanz umgewandelt werden.
  7. Verfahren nach Anspruch 6, worin zwischen 75 und 90 % des der bipolaren Membran-Elektrolyse-Zelle zugeführten Salzes in Reagens zur Umlaufführung in den Schritt (d) und in die zurückgewonnene gelöste Substanz umgewandelt werden.
  8. Verfahren nach irgendeinem der Ansprüche 1, 2 und 4 bis 7 zur Rückgewinnung der schwachen organischen Säure Phenol aus einem wäßrigen Speisestrom, worin das Reagens für die Ionisierung in der dispergierten Phase Natriumhydroxid unter Bedingungen ist, unter denen mehr als 90 % des in dem Speisestrom vorhandenen Phenols entfernt werden.
EP89109877A 1988-06-02 1989-06-01 Rückgewinnung und Konzentration von wässerigen Säuren und Basen Expired - Lifetime EP0344760B1 (de)

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US07/201,632 US4839056A (en) 1988-06-02 1988-06-02 Recovery and concentration of aqueous acids and bases
US201632 1988-06-02

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DE3926059C2 (de) * 1989-08-07 1998-01-29 Basf Ag Phosphonomethylierte Polyvinylamine, Verfahren zu ihrer Herstellung und ihre Verwendung
DE3929137C1 (de) * 1989-09-01 1991-02-28 Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung Ev, 8000 Muenchen, De
DE3935831A1 (de) * 1989-10-27 1991-05-02 Hoellmueller Maschbau H Anlage zur herstellung von durchkontaktierten leiterplatten und multilayern
US5753097A (en) * 1996-10-03 1998-05-19 Sachem, Inc. Process for purifying hydroxide compounds

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US3111472A (en) * 1957-08-24 1963-11-19 Zaidan Hojin Noguchi Kenkyu Jo Process of carrying out electrochemically electrolysis
US3617546A (en) * 1970-04-13 1971-11-02 Exxon Research Engineering Co Removal of organic compounds by liquid membrane
US4283290A (en) * 1977-07-06 1981-08-11 Davy International (Oil & Chemicals) Ltd. Purification utilizing liquid membrane with electrostatic coalescence
DE3020104A1 (de) * 1980-05-27 1981-12-03 Merck Patent Gmbh, 6100 Darmstadt Verfahren zur herstellung von diacetonketogulonsaeure
EP0121611B1 (de) * 1983-03-14 1990-04-25 AlliedSignal Inc. Säurebildung in Laugen mit gleichzeitiger Herstellung von Alkalimetall-Hydroxid und Salzsäure durch Wasserzersetzung in einem aus drei Kammerntypen bestehenden Elektrodialyseapparat

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DE68913811T2 (de) 1994-09-22
US4839056A (en) 1989-06-13
DE68913811D1 (de) 1994-04-21
ES2053867T3 (es) 1994-08-01
EP0344760A2 (de) 1989-12-06
ATE102849T1 (de) 1994-04-15

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